Pension and Other Postretirement Benefits (Funded Status of Pension Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Pension plans that have assets in excess of their accumulated benefit obligations with those whose assets are less than their obligations
Plans with assets in excess of accumulated benefit obligation, Plan Assets	$ 53	$ 52
Plans with accumulated benefit obligation in excess of assets, Plan Assets	573	553
Total, Plan Assets	626	605
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	50	49
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	710	640
Total, Accumulated Benefit Obligation	760	689
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	52	50
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	835	735
Pension Benefits [Member]
Pension plans that have assets in excess of their accumulated benefit obligations with those whose assets are less than their obligations
Total, Plan Assets	626	605	573
Total, Projected Benefit Obligation	887	785	783
Medical and Life Insurance Benefits [Member]
Pension plans that have assets in excess of their accumulated benefit obligations with those whose assets are less than their obligations
Total, Plan Assets	0	0	0
Total, Projected Benefit Obligation	$ 57	$ 69	$ 74